1. Field of the Invention
The present invention relates to a vehicle recognition device configured to identify a pair of lights on both sides of a vehicle in an image, which is obtained through an imaging unit, as a first characteristic region and a second characteristic region.
2. Description of the Related Art
Hitherto, there has been known a vehicle recognition device adapted to recognize, for example, the width of the rear part of a vehicle. The vehicle recognition device has a means for identifying a first characteristic region and a second characteristic region, which are formed of pixels having pixel values in a predetermined range and which are arranged in a horizontal direction in an image obtained through an imaging unit (refer to for example, Japanese Patent Application Laid-Open No. 2009-230530 (hereinafter referred to as “Patent Document 1”). The first and the second characteristic regions are highly likely to correspond to a pair of brake lights located on both sides of the rear part of the vehicle, thus making it possible to recognize the width or the like of the vehicle on the basis of the first and the second characteristic regions.
The vehicle recognition device described in Patent Document 1 has a characteristic region determining means, which determines whether the first and the second characteristic regions belong to regions of the same vehicle, in order to enhance recognition accuracy. For the purpose of the determination, a first determination region is set in a vertical peripheral area of the first characteristic region or a peripheral area in the direction of the second characteristic region, and a second determination region is set at a position that is line-symmetrical to the first determination region relative to the centerline of the first and the second characteristic regions. If the degree of correlation between the first determination region and the second determination region is high, then the determining means determines that the first and the second characteristic regions are regions of the same vehicle.
However, in the vehicle recognition device described above, a brake light of a preceding vehicle and a brake light of a vehicle preceding that vehicle may overlap in an image received from the imaging unit. In this case, according to the aforesaid vehicle recognition device, even if the brake lights are detected as described above at night, the image of the brake light of the vehicle that precedes the preceding vehicle may be combined with the image of the brake light of the preceding vehicle, resulting in the detection of a larger width in the horizontal direction of the brake light of the preceding vehicle.
In this case, the value of the width of the preceding vehicle or the distance to the preceding vehicle calculated on the basis of the images of the brake lights may considerably deviate from an actual value, leading to a possibility of failure to accurately recognize the width or the like of the preceding vehicle.